A novel theoretical model is proposed to study the continuum damage mechanical (CDM) behavior of reinforced thermoplastic pipes (RTPs) under bending moments, in which stress analysis of composites, failure evaluation and stiffness degradation are combined in loop calculation. Based on the existing homogenization assumption, the stress distribution of every ply could be calculated according to the equilibrium equations between the RTP and a hypothetical homogenous pipe. Once stresses of composite plies satisfy Hashin-Yeh failure criterion, dominant failure modes are determined by filtering failure coefficients. Subsequently, the stiffness degradation model would be performed, in which a sine weight function is employed to consider the damage distribution along the hoop direction. Meanwhile, the von Mises criterion and Ramberg-Osgood curve are used to simulate the material nonlinearity of liner and coating. Four-point bending tests and numerical simulations were conducted to verify the proposed theoretical model. A user-defined VUMAT subroutine was employed to simulate the progressive failure of 3D composites. Compared with experimental tests and numerical simulations, the proposed model could give accurate predictions on the linear and nonlinear responses, such as the bending stiffness, the stress field and the damage propagation. Furthermore, different methods for the four-point bending test were also compared and good correlation found.

The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments. To investigate the collapse of RTPs, numerical simulations and hydrostatic pressure tests are conducted. For the numerical simulations, the eigenvalue analysis and Riks analysis are combined, in which the Hashin failure criterion and fracture energy stiffness degradation model are used to simulate the progressive failure of composites, and the “infinite” boundary conditions are applied to eliminate the boundary effects. As for the hydrostatic pressure tests, RTP specimens were placed in a hydrostatic chamber after filled with water. It has been observed that the cross-section of the middle part collapses when it reaches the maximum pressure. The collapse pressure obtained from the numerical simulations agrees well with that in the experiment. Meanwhile, the applicability of NASA SP-8007 formula on the collapse pressure prediction was also discussed. It has a relatively greater difference because of the ignorance of the progressive failure of composites. For the parametric study, it is found that RTPs have much higher first-ply-failure pressure when the winding angles are between 50° and 70°. Besides, the effect of debonding and initial ovality, and the contribution of the liner and coating are also discussed.

This paper investigates the burst failure of reinforced thermoplastic pipes (RTPs) via combined experimental and numerical research. Two completely different burst forms appeared during the experiments. The dry burst form occurs with matrix cracks, fiber breakage and crack of liner and coating, which is a common burst morphology. A new burst morphology, which is never reported in open literature, is observed in the experiments. This burst morphology, defined as wet burst form, presents a long dent in the coating and invisible composite damage. In order to simulate the burst failure of RTPs, a numerical model was proposed, in which element removal criteria and the nonlinear stiffness degradation model based on Hashin-Yeh failure criterion were employed to conduct progressive failure analysis on 3D composites. It was found that the wet burst form has lower burst pressure and causes larger damaged area, which is more dangerous in engineering. For the damage propagation, progressive failure occurs on middle composites and induces the final burst when the dry burst form occurs. As for the wet burst form, water flows into the middle of RTPs, which causes the delamination, matrix crack and bulge of coating. During the process, fibers play few roles in bearing loads.

Due to the anisotropy and progressive failure of composites, the collapse problem of RTPs is more complex compared with that of traditional steel pipes. To address this problem, the collapse behavior of RTPs subjected to external pressure was studied by conducting collapse tests and numerical simulations. Two different collapse modes including the O-type and U-type mode were observed during the collapse tests. It was the first time to observe the U-type collapse mode of RTPs in open literature. For O-type collapse mode, the cross-section turned into an ellipse. And for U-type collapse mode, it turned heart-shaped. Meanwhile, numerical simulations were conducted by combing eigenvalue analysis and arc-length method, in which the progressive failure of composites was considered by employing a fracture energy degradation model based on the Hashin criterion. To simulate the U-type collapse mode, eccentricity was also introduced. Research results indicated that the critical pressure obtained by tests and numerical simulations agreed well for both O-/U-type collapse modes. The collapse process could be described as "contraction-collapse point-large deformation". It was found that the progressive failure of composites would reduce the pressure-resisting capacity greatly. For the composites, the shear failure, the matrix and fiber compressive failure were dominant failure modes.

This paper investigates the bending stiffness and progressive failure of reinforced thermoplastic pipes (RTPs) under bending loads, in which a theoretical method based on the strain energy equivalence of multi-layered anisotropic cylinders, is proposed. The bending stiffness and stress field was derived from the equilibrium between the work done by bending moments and the strain energy. This new method could consider the hybrid of isotropic and anisotropic materials and improve computation efficiency significantly. To verify the theoretical method, Abaqus/Explicit quasi-static analysis on 3D composite elements was performed, in which the progressive failure was considered by using a VUMAT subroutine. The degradation of composites was implemented by a nonlinear stiffness degradation model based on the Hashin-Yeh failure criterion. The comparison showed that the theoretical results are slightly conservative as the theoretical method neglects the contribution of interlayer interactions. Meanwhile, it can accurately predict the dominant stresses of each composite lamina. According to numerical simulations, the fiber tensile failure, the matrix tensile and compressive failure are the dominant failure modes of RTPs under bending loads. Furthermore, the effects of the winding angles of fibers on damage propagation and the effects of the initial ovality on the bending stiffness are also discussed.

In the present study, the collapse behavior of RTPs was analyzed by an experimentally-verified numerical method, in which the eccentricity directions, the combinations of eccentricity and initial ovality are considered. Eigenvalue analysis and Riks analysis were combined to simulate the progressive failure of composites during the collapse, which was conducted by a continuum damage model based on Hashin failure criterion and fracture energy dissipation. The stress analysis showed that the hoop stress of composites is much higher than that of isotropic layers both in the elastic and progressive failure phases. Because of this, thick composites always play important roles in bearing external pressure. Except the experimentally observed O-/U-type collapse modes, the C-type collapse mode was observed and simulated for the first time. They all go through the uniform contraction-collapse-large deformation process, and have the same failure modes of composites. However, different from the O-/U-type collapse modes, the cross-sectional deformation of the C-type collapse is not symmetrical and has a moving maximum-displacement point. The collapse pressure decreases linearly as the increase of the eccentricity and the initial ovality. The effect of eccentricity directions can be concluded as: more dispersed eccentricity distribution makes composites contribute more to the pressure resistance.

以一种黏结型的纤维增强柔性管为研究对象,基于ABAQUS/Explicit建立纤维增强柔性管的实体单元模型,根据Hashin-Yeh失效判据判断柔性管模型失效情况,使用了嵌套非线性刚度退化模型的VUMAT子程序,发展了轴向压缩下纤维增强柔性管的渐进失效模型,具有准确判断柔性管在压缩工况下失效模式、位置的功能.通过压缩实验验证了有限元模型,数值模拟与实验得到的力与位移关系吻合较好.在此基础上进一步分析了压缩工况下,柔性管各失效模式的演化过程.研究结果表明:压缩工况下,纤维增强柔性管失效的主要模式为基体压缩及纤维压缩失效,且各失效模式出现于管道的不同位置.柔性管纤维缠绕角度大于 30°时,主要的失效模式由纤维压缩失效变为基体压缩失效.

Torsional characteristics must be considered in the mechanical analysis of offshore pipelines. However, there is no specific theoretical model for RTPs to predict the torsional behavior due to the multilayered helically winding laminates. To address the problem, a theoretical model using the energy method is constructed, in which the governing equation is based on the strain energy-work equivalence of helically anisotropic hollow cylinders instead of homogenous structures in previous studies on unbonded flexible risers. The strain energy of RTPs is firstly obtained by the stress analysis of helically anisotropic elements, while the work is derived by the torsion-deformation relationship. It gives a concise theoretical expression of torsional stiffness of RTPs for the first time and greatly improves the computation efficiency. Another improvement is that it could consider the coexistence of the isotropic and orthotropic materials due to the symmetry of isotropic materials. To verify the proposed model, quasi-static torsion tests and numerical simulations were conducted on two RTP specimens. The proposed model could give accurate torsional stiffness predictions in both twisting directions. Besides, the stress distributions, the effect of thickness-radius ratios and fiber's winding angles were also investigated, in which the applicability of the proposed model was further discussed.

The accurate prediction of bending stiffness is important to analyze the buckling and vibration behavior of reinforced thermoplastic pipes (RTPs) in practical ocean engineering. In this study, a theoretical method in which the constitutive relationships between orthotropic and isotropic materials are unified under the global cylindrical coordinate system is proposed to predict the bending stiffness of RTPs. Then, the homogenization assumption is used to replace the multilayered cross-sections of RTPs with homogenized ones. Different from present studies, the pure bending case of homogenized RTPs is analyzed, considering homogenized RTPs as hollow cylindrical beams instead of using the stress functions proposed by Lekhnitskii. Therefore, the bending stiffness of RTPs can be determined by solving the homogenized axial elastic moduli and moment of inertia of cross sections. Compared with the existing theoretical method, the homogenization method is more practical, universal, and computationally stable. Meanwhile, the pure bending case of RTPs was simulated to verify the homogenization method via conducting ABAQUS Explicit quasi-static analyses. Compared with the numerical and existing theoretical methods, the homogenization method more accurately predicts the bending stiffness and stress field. The stress field of RTPs and the effect of winding angles are also discussed.

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

An analytical model is presented to predict the progressive failure of reinforced thermoplastic pipes (RTPs) under axial compression, in which the existing homogenization method and a nonlinear stiffness degradation model are combined to predict the continuum damage mechanical response in an iterative and cyclic way. As the homogenization method ignores the effect of the cross-sectional curvature on the damage sequence, a stress correction factor is defined to consider this effect. Once corrected stresses satisfy Hashin-Yeh failure criteria, the nonlinear stiffness degradation model is adopted to update the constitutive relationship established by the homogenization method. The proposed model is capable of identifying the damage location and failure mode, analyzing damage accumulation and predicting the ultimate compression. Meanwhile, ABAQUS Explicit quasi-static analyses calling a user-defined subroutine were conducted to capture the progressive failure mechanisms in 3D composites and verify the proposed model. The proposed model was found to give accurate prediction on the elastic stiffness, first ply failure, the damaged stiffness, the ultimate compression, and stress distributions. Furthermore, the effects of fiber's winding angles and the thickness-radius ratios have been discussed, which illustrate that tensile failure mode would appear even when RTPs are under axial compression.

区域约束混凝土结构的抗压、抗剪、抗震和延性均优于传统混凝土梁.基于区域约束应变-应力模型对混凝土梁结构力学性能特征分析,获得混凝土损伤塑性模型;结合高斯积分求解损伤因子与ABAQUS有限元软件,构建区域约束混凝土梁非线性有限元分析模型,模拟区域约束混凝土梁构件的受力过程.研究结果表明,随着受力时间的增多,区域约束混凝土梁损伤情况越严重,损伤最为严重的是跨中受弯部区域与支座受剪区域,损伤值高达0.9994.经测试,该有限元模型的分析结果可信度极高,可作为后期混凝土研究领域的借鉴方法.

为了优化乳化沥青冷再生混合料适宜的乳化沥青和水泥掺量范围,基于室内模拟现场钻芯试验、湿轮磨耗试验,研究了乳化沥青和水泥掺量下冷再生混合料的初期和终期抗松散性能,采用力学性能试验、路用性能试验和疲劳性能试验优化了设计用于乳化沥青冷再生混合料的最佳乳化沥青用量和水泥掺量.结果表明,乳化沥青和水泥掺量对冷再生混合料的早期钻芯完整性、抗松散性能、力学性能、路用性能与疲劳性能均有显著改善作用.随着乳化沥青用量的增大,冷再生混合料力学性能、路用性能与疲劳特性均存在峰值.增大水泥掺量能够显著提高冷再生混合料的水稳定性和高温稳定性及低应力水平下的疲劳寿命,但是过多的水泥掺量导致乳化沥青冷再生混合料刚性增大、柔韧性降低、高应变水平下的疲劳寿命减低.根据优化结果,推荐1.5％～2.0％水泥、3.5％～4％乳化沥青为最佳配比.

Axial compression tests were carried out on 6 square steel tube confined concrete short columns and 6 BFRP square pipe confined concrete axial compression tests. The concrete strength grades were C30, C40, and C50. The test results show that the failure modes of steel pipe and BFRP pipe are obviously different, and the BFRP pipe undergoes brittle failure. Compared with the short columns of concrete confined by BFRP pipes, the ultimate bearing capacity of axial compression is increased by -76.46%, -76.01%, and -73.06%, and the ultimate displacements are -79.20%, -80.78%, -71.71%.

针对当前方法存在单调荷载作用下位移曲线的变化与实际结果吻合度低、在大变形下混凝土框架结构的受力特性较差的问题,提出基于有限元分析的高性能泵送混凝土框架结构变形研究方法.首先,简单介绍了混凝土框架结构的受力特点;其次,通过内力来确定混凝土的预应力配筋,获得使用荷载时的性能参数,构建混凝土框架横梁各段曲线方程,当正负等效荷载总和等于零时,可以减小混凝土框架结构梁端反力给柱轴力所带来的影响,在此基础上,对混凝土框架结构的最大裂缝进行计算,能够得到混凝土框架构件的等效应力等条件;最后,利用有限元构建混凝土框架结构的平衡方程,对高性能泵送混凝土框架结构变形进行分析.最终实现了对高性能泵送混凝土框架结构变形研究.试验结果得到,在对高性能泵送混凝土框架结构变形研究时,提出方法在单调荷载作用下位移曲线的变化更接近实际结果,并且在大变形下混凝土框架结构的受力特性较好,验证了提出方法的有效性.

通过改变圆钢管混凝土短柱的宽厚比和膨胀剂掺量,即混凝土膨胀剂掺量为0％、4％、6％、8％,圆形钢管外径为200 mm、250 mm,制作10个试件,分为A、B两组,对其进行轴压试验,观察其破坏形态,得到了不同宽厚比及膨胀剂掺量下的σ-ε曲线和极限承载力.研究结果表明,管内混凝土中的膨胀剂掺量为4％、6％和8％的圆钢管混凝土柱的轴压极限承载力相比于普通圆钢管混凝土柱的极限承载力,A组分别提高46.88％、35.56％和13.73％,B组分别提高53.13％、41.58％、20.08％.采用ABAQUS非线性有限元软件模拟分析,与试验结果模拟较为吻合.因此,当管内混凝土中的膨胀剂掺量在4％时,圆钢管混凝土柱的极限承载力提高幅度最大,性能最优.

因为混凝土优良的性能使其具有诸多优势,所以被广泛地应用于工程建设中.但是混凝土在使用中会受到多方面的因素的制约,比如使用年限、外部的干扰、内部的膨胀等,这些影响会大大降低混凝土的使用效能.所以,只有定期地对混凝土结构进行维护管理,同时还应该制定一个完美的加固计划,才能确保工程的安全和稳定性.基于此,笔者把混凝土结构加固作为本文的探讨对象,介绍了现在的加固技术,同时分析应用,以期为相关的工作人员提供有价值的建议.

为了改善再生骨料混凝土在工程运用中的显著缺点,利用区域约束混凝土的优点,将再生骨料混凝土与区域约束结合起来,形成区域约束再生混凝土,由于约束机制的变化,使得再生混凝土的承载力、延性等力学性能得到有效改善.

我国的建筑结构在飞快地发展,为了给人们的生活提供便捷的服务,近年来基础设施建设投入逐年增多,该项目的建设上升趋势明显,高层及超高层建筑越来越多这就要求我们在材料及技术上面得以创新.文章从约束混凝土的历史进程、箍筋对于约束混凝土的影响、高强箍筋约束混凝土、区域约束混凝土等几个方面进行分析,通过前几个方面进行阐述了它们各自的优缺点以及存在的问题,再到后来区域约束混凝土的思想被提出,区约约束混凝土的优点,它可以解决之前普通约束混凝土所面临的一些问题.